Microelectromechanical systems (MEMS) include mechanical and electrical components having dimensions in the order of microns or smaller. MEMS structures are used in numerous applications including microsensors and microactuators. Microsensors can be used to sense and/or measure pressure, flow, acceleration, temperature and stress, amongst other conditions. A microsensor functions by generating electrical signals in response to an input condition such as flow, pressure or temperature on the sensor. The sensor may be calibrated such that the electrical signal and, thus the movement of the mechanical component, can be correlated to the condition.
The ability to detect the presence of air flow can be a key element of many systems and devices. MEMS based flow sensors can be utilized for measuring flow rates in a variety of commercial, industrial and medical applications. Various medical, process, and industrial applications, ranging from portable ventilators supplying pressurized air or respiratory treatments to large-scale processing plants in a chemical plant require the use of flow sensors. In such applications, flow control is an inherent aspect of proper operation, which can be achieved in part by utilizing flow sensors to measure the flow rate of fluid within a flow system. The flow sensor is typically deployed by placing it directly in the flow stream, which makes the flow sensor wire bonds, or sensing elements damaged by debris, lint, or from patient mishandling.
The problem with prior art flow sensor arrangements and relationships is that the wire bond pads and active regions of the sense die end up facing the sensed media. Water or other contaminants can attack the sense die and its wire bonds. Additionally, conventional flow sensor configurations lack the ability to sense ultra-low flow liquid.
Based on the foregoing it is believed that a need exists for an improved MEMS based flow sensor for protecting the sense die and its wirebonds from the flow stream, by attaching the flow channel structure to the backside of the sense die. It is believed that by utilizing the flow sensor described in greater detail herein, ultra-low flow liquid can potentially be sensed.